1. Field of the Invention
The present invention relates generally to electroplating of single metals and alloys, and more particularly to electroplating of nickel-iron (Ni-Fe) alloy for example, and more specifically to a plating method of electroplating a uniform Ni-Fe composition alloy of film on a magnetic film such as an 80:20 Ni-Fe magnetic core thin film for use in a magnetic recording head for example.
2. Description of the Prior Art
A nickel-iron plated film used as a magnetic film has its magnetic properties severely varied depending on alloy compositions. Referring to FIG. 1, there is illustrated an interrelation between iron weight composition (wt %) and pH value of a plating solution, those pH values being a factor to influence the alloy composition. As the pH of the plating solution is raised, the iron weight composition (wt %) in the plating alloy is increased, the iron weight composition (wt %) has its maximum Fe when the pH is i.sub.2, around which there is provided a smooth characteristic curve with reduced variations of the iron weight composition.
For bringing the alloy composition into its most stabilized state, selection may be made of the least variations of the iron weight composition with respect to the variations of the pH of the plating solution, say, a pH value i.sub.2 of the plating solution. Accordingly, prior practice of the plating adopted such a pH of a plating solution that the iron weight composition is maximum.
With such prior practice where metal is plated under a pH of a plating solution selected conventionally, iron ion concentration in the plating solution is decreased following the deposition of a plated film and hence an iron weight composition in the plated film is also decreased, so that iron ion must be replenished into the plating solution during the plating to assure uniform components in the direction of film thickness. The prior practice therefore surffers from difficulties that there is required an additional dropping device using a high precision constant capacity pump as well as requiring much labor for its operation, followed by a difficulty in reliability and reproducibility on whether or not uniform components have been yielded in the direction of film thickness.